Determining of Velocity Fields During Real and Experimental Simulated Beer Fermentations by UDV and LDA

Abstract Beer fermentation is a very complex process, especially in the fluid‐mechanical and the biochemical point of view. Our aim is to optimize the fermentation by flow control, which requires quantities of data. The applied velocity measuring techniques should be non‐invasive to ensure that neither the flow nor the fermentation in the green beer gets influenced. Therefore, an Ultrasonic Doppler Velocimetry (UDV) system is used to determine velocity fields with 128 measuring points. It works in the turbid fluid with the existing yeast cells as tracer particles and can be applied easily to the industrial scale. For the validation of CFD‐codes and the better understanding of measurements and flow processes, model fluids are used. They can be adapted to real fluid properties like density and viscosity and allow measurements with Laser Doppler Anemometry (LDA). Another advantage over the real fluid is their fixed composition, which leads to negligible natural variations. All experiments are performed in a 270 litre fermenter. Besides the real process, measurements through optical access points and the simulation of fermentations with CO 2 and heat emission are enabled. Eight individually controllable cooling zones are used as thermal actors. Resulting changes in boundary conditions induce temperature gradients and hence allow to control the flow inside the tank. This work deals with the experimental set‐up and the results on the one hand and a comparison between real and simulated fermentations on the other hand. Special attention is given to investigations of the multi‐phase flow inside the vessel and the effects of changing constraints. The usability of UDV measurement techniques is the key benefit in this case, because it can be used in green beer and model fluids and does not influence the flow. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)